Power transmission belt and method for fabricating the same

ABSTRACT

Short aramid fibers extruded from a side face of each rib in a V-ribbed belt are formed in curled shape. The root portions of the extruded short aramid fibers are raised from the side face of the rib. The tip portion of each extruded short aramid fiber is bowed in a direction different from a bowing direction of its medial portion. The extruded sections of the short aramid fibers are different in bowing direction from one another to decentralize the orientation thereof.

BACKGROUND OF THE INVENTION

This invention relates to a power transmission belt and method forfabricating the same, and particularly relates to a power transmissionbelt such as a V-ribbed belt or a V-belt including short fibers mixedinto its compression rubber and a method for fabricating the same.

As disclosed in Japanese Patent Application Laid-Open Gazettes Nos.3-219147 and 7-4470, there are conventionally known power transmissionbelts in which a crowd of short fibers are mixed into their compressionrubber in a manner to be oriented along the width of the belt and someof the short fibers are extruded from the surface of the compressionrubber. Power transmission belts of such kind aim at enhancing bearingstrengths and wearing properties of their friction drive sections andpreventing noise production during their running.

However, even such a power transmission belt out of which some of theshort fibers extrude, if the total area of extruded sections of theshort fibers occupying the surface of the compression rubber is small,cannot enhance its wearing property so much because the area of thecompression rubber in direct contact with a pulley becomescorrespondingly large.

For the purpose of increasing the exposure areas of short fibers withrespect to the surface area of the compression rubber, Japanese PatentApplication Laid-Open Gazette No. 1-164839 has proposed a powertransmission belt as shown in FIG. 19. In this power transmission belt,extruded sections 102 of short aramid fibers 101 mixed into acompression rubber 100 are 0.065 to 0.13 mm long, longer than those ofconventional short fibers, and are bent in a particular direction 103along a working flank of the belt.

In such a power transmission belt, though the exposure areas of shortfibers 101 can be increased, the extruded sections 102 are bent at theirroots and therefore made substantially flush with the surface of thecompression rubber 100. Accordingly, the extruded sections 102 aredifficult to together form surface unevenness as considered aseffectively suppressing noise. This invites a problem that the effect ofsuppressing noise cannot sufficiently be obtained.

Furthermore, since the extruded sections 102 of short fibers are bent inthe particular direction 103 along the surface of the compression rubber100, running the belt in a reverse direction would largely changeproperties of the belt. Therefore, in order for the belt to obtain itsproperties as designed, the belt must be checked carefully on itsrunning direction at the time of fitting to pulleys. In addition, thisconventional belt is not applicable to devices capable of convenientlyswitching the running directions of the belt.

Moreover, if the length for which the short fiber is extruded from thesurface of the compression rubber 100 is too large, the belt willlargely change its properties when the extruded sections 102 are reducedby abrasion. Therefore, considering to maintain desired belt propertiesconstant for a long time, there is a limit to the extruded length of theshort fiber. Accordingly, it has been desired to make great strides inenhancing the performance of the belt by improving not only short fibersbut also the compression rubber 100.

In view of these problems, an object of the present invention is toprovide a power transmission belt excellent in wearing property, hard toproduce noise and independent of its running direction.

Another object of the present invention is to further enhance theperformance of the belt by improving the surface configuration of thecompression rubber.

SUMMARY OF THE INVENTION

To attain the above first object, a power transmission belt of thepresent invention is constructed so that extruded sections of shortfibers are formed in curled shape.

More specifically, a power transmission belt of the present invention isdirected to a power transmission belt in which a crowd of short fibersare mixed into a compression rubber thereof in a manner to be orientedin a given direction and some of the short fibers each have an extrudedsection extruded from a surface of the compression rubber, and ischaracterized in that the extruded section of the short fiber is raisedfrom the surface of the compression rubber and then bowed.

With this construction, since the extruded sections of the short fibersare bowed, they have sufficiently large exposure areas with respect tothe surface area of the compression rubber, resulting in enhancedwearing property of the compression rubber. Further, since some of theshort fibers are raised from the surface of the compression rubber,their root portions are not born against but kept off from the surfaceof the compression rubber. Accordingly, microscopic unevenness is formedover the surface of the compression rubber so that the root portions ofshort fibers constitute microscopic convexities, thereby suppressing theoccurrence of noise.

The extruded section of the short fiber is preferably bowed first in onedirection and then another direction on the way from root to tipthereof.

With this construction, when the belt is entrained about a pulley, theshort fibers exert restoring forces like a leaf spring on the pulley. Asa result, the restoring forces can absorb variations in belt tensionassociated with the running of the belt. Accordingly, the belt cantransmit power with stability, i.e., the belt can stabilize its powertransmission performance. Also, though the pressures to be applied tothe short fibers will become larger with increase in bearing stress onthe surface of the compression rubber, the stresses placed on the rootportions of the short fibers can be relaxed by the restoring forces ofthe bowed portions of the short fibers. Accordingly, the short fiberscan be prevented from dropping out of the compression rubber, whichenhances the wearing property and elongates the life time of the belt.

At least the tip of the extruded section of the short fiber ispreferably flattened. In this case, the surface area of each short fibercan be increased thereby enhancing the wearing property of the belt.

The tip of the extruded section of the short fiber may be cracked. Alsoin this case, the surface area of each short fiber can be increasedthereby enhancing the wearing property of the belt.

The extruded sections of the short fibers are preferably different inbowing direction from one another to decentralize the orientationthereof.

With this construction, since the extruded sections of the short fibersare different in bowing direction from one another to decentralizedtheir orientation, this makes it possible to exhibit the wearingproperty of the belt uniformly in every direction. Therefore, even ifthe belt is run in a reverse direction, its properties do not change. Inother words, the belt has no dependency on its running direction.Accordingly, the compression rubber of the belt can exhibit uniformbearing strength and wearing property in either running directionindependent of the running direction of the belt.

The short fiber may be made of para-aramid fibers or meta-aramid fibers.In these cases, suitable short fibers can be obtained.

To attain the above second object, a power transmission belt of theinvention is constructed so that unevenness is provided in the surfaceof the compression rubber to increase its entire surface area.

Specifically, in the power transmission belt, the surface of thecompression rubber is preferably formed in uneven configuration.

With this construction, since the surface of the compression rubber isformed unevenly, its entire surface area can be increased. This enhancesthe performance of the belt. In addition, clearances are likely to beformed between contact surfaces of the belt and a pulley. Accordingly,even if water or the like enters between the belt and pulley, it can bedistributed or discharged through the clearances, which stabilizesfrictional resistance of the belt.

The surface unevenness of the compression rubber is preferably formed inwavy shape. Thereby, a suitable uneven configuration can be formed inthe surface of the compression rubber.

The surface unevenness of the compression rubber is preferably formed tohave a level difference of 0.5 to 10 μm. Also in this case, a suitableuneven configuration can be formed in the surface of the compressionrubber.

A method for fabricating a power transmission belt of the presentinvention is directed to a method for fabricating a power transmissionbelt in which some of a crowd of short aramid fibers are extruded from asurface of a compression rubber, and is characterized by comprising thestep of grinding the compression rubber into which the crowd of shortaramid fibers are mixed in a manner to be oriented in a given directionwith a grinding wheel having super abrasives extruded for 50 to 95% ingrain size thereof from the surface of the grinding wheel.

According to this method, since the height of extrusion of each of thesuper abrasives is large, a bonding part for the super abrasives in thegrinding wheel is prevented from direct contact with the compressionrubber of the power transmission belt, there by suppressing productionof frictional heat. Accordingly, the grinding step can be carried outunder extended conditions such as increase in the grinding speed.Further, the length for which each of the short aramid fibers isextruded from the surface of the compression rubber can be easilyincreased. This facilitates the bowing of the extruded sections. Inaddition, such a large height of extrusion of the super abrasive canfacilitate to form the surface of the compression rubber into unevenconfiguration.

Another method for fabricating a power transmission belt of the presentinvention is also directed to a method for fabricating a powertransmission belt in which some of a crowd of short aramid fibers areextruded from a surface of a compression rubber, and is characterized bycomprising the step of grinding the compression rubber into which thecrowd of short aramid fibers are mixed in a manner to be oriented in agiven direction with a grinding wheel having super abrasives the densityof which is 3.5 to 55%.

According to this method, since the density of the super abrasives issmall, chip pockets can be increased so that grinding chips can bereadily expelled. Therefore, clogging between the abrasives due to thechips is difficult to occur. Accordingly, it can be suppressed that suchclogging increases grinding load and produces heat in a grindingsurface. As a result, the grinding step can be carried out underextended conditions. Further, since the short aramid fibers extruded outof the compression rubber are hardly cut, this facilitates the formationof extruded fiber sections of long length and the bowing of the extrudedfiber sections. In addition, such a small density of the super abrasivescan facilitate to form the surface of the compression rubber into unevenconfiguration.

Still another method for fabricating a power transmission belt of thepresent invention is also directed to a method for fabricating a powertransmission belt in which some of a crowd of short aramid fibers areextruded from a surface of a compression rubber, and is characterized bycomprising the step of grinding the compression rubber into which thecrowd of short aramid fibers are mixed in a manner to be oriented in agiven direction with a grinding wheel having super abrasives which areeach extruded for 50 to 95% of grain size thereof from the surface ofthe grinding wheel and the density of which is 3.5 to 55%.

According to this method, since the height of extrusion of each of thesuper abrasives is large and the density thereof is small, increase ingrinding load and heat production in a grinding surface can besuppressed. Accordingly, the grinding step can be carried out underextended conditions. Further, it can be facilitated to increase thelength for which each of the short aramid fibers is extruded from thesurface of the compression rubber and bow the extruded fiber sections.In addition, since the density of the super abrasives is small, chippockets are large in size so that grinding chips can be readilyexpelled. Therefore, clogging between the abrasives due to the chips isdifficult to occur.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a V-ribbed belt according toEmbodiment 1 of the present invention.

FIG. 2 is a cross-sectional view showing the vicinity of the surface ofa rib.

FIG. 3 is a schematic view showing an extruded section of a short aramidfiber.

FIG. 4 is a schematic view showing a tip of the extruded section of theshort aramid fiber.

FIG. 5 is a schematic view showing the structure of a grinding apparatusfor a V-ribbed belt.

FIG. 6(a) is a partly enlarged plan view showing the periphery of agrinding wheel and FIG. 6(b) is a cross-sectional view taken along theline A—A of FIG. 6(a).

FIG. 7 is a schematic view showing the structure of a testing device fora performance comparison test.

FIG. 8 is a graphic representation of performance comparison ofinventive and prior-art V-ribbed belts with reference to variations intension ratio in their initial conditions.

FIG. 9 is a graphic representation of performance comparison of theinventive and prior-art V-ribbed belts with reference to variations intension ratio in their conditions where the belts have been continuouslyrun for 24 hours.

FIG. 10 is a graphic representation of performance comparison of theinventive and prior-art V-ribbed belts with reference to chattering.

FIG. 11 is a cross-sectional view of a V-ribbed belt according toEmbodiment 2 of the present invention.

FIG. 12 is an enlarged view of the surface of a rib.

FIG. 13 is an enlarged cross-sectional view showing an example of thevicinity of the surface of the rib.

FIG. 14 is an enlarged cross-sectional view showing another example ofthe vicinity of the surface of the rib.

FIG. 15 is a schematic view showing the structure of a testing devicefor another performance comparison test.

FIG. 16 is a graphic representation of performance comparison ofinventive and comparative V-ribbed belts with reference to frictionalforces.

FIG. 17 is a graphic representation of performance comparison of theinventive and comparative V-ribbed belts with reference to frictionalforces under water-inpouring conditions.

FIG. 18 is a cross-sectional view of a joined V-ribbed belt.

FIG. 19 is a view showing how a conventional power transmission belt hasshort aramid fibers extruded.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described withreference to the drawings.

Embodiment 1

FIG. 1 shows a cross section of a power transmission belt 10 accordingto Embodiment 1 of the present invention. The power transmission belt 10is a V-ribbed belt used for automotive engine auxiliary driving devicesor other general industrial applications.

A tension member 2 extending along the length of the belt 10 is embeddedin an adhesion rubber layer 4 in a manner to be arranged at regularintervals along the width of the belt 10 (in the lateral direction ofFIG. 1). A fabric layer 5 is provided on the upper face side of theadhesion rubber 4, i.e., on the back face side of the belt 10. Aplurality of ribs 7,7, . . . are provided along the width of the belt 10on the lower face side of the adhesion rubber 4, i.e., on the bottomface side of the belt 10, to extend along the length of the belt 10. Theplurality of ribs 7,7, . . . correspond to a “compression rubber” towhich reference has been made in this description. The adhesion rubberlayer 4 and the ribs 7 may be made of, for example, chloroprene rubber,H-NBR rubber, CSM rubber, natural rubber, SBR rubber, butadiene rubber,EPM or EPDM.

A plurality of short aramid fibers 8, 8, . . . are embedded in each ofthe ribs 7, 7, . . . while maintaining their orientation to a givendirection. Particularly in this invention, the short aramid fibers 8, 8,. . . are embedded in each of the ribs 7, 7, . . . while maintainingtheir orientation to the belt widthwise direction. The short aramidfiber 8 may be made of a para-aramid or meta-aramid fiber. In otherwords, poly-para-phenyleneterephthalamide orpoly-meta-phenyleneisophthalamide is applicable for the short aramidfiber 8. More specifically, Kevlar (trademark of E.I. Du Pont de Nemours& Co.), Technora (trademark of Teijin Ltd.), Twaron (trademark of EnkaB.V.) or the like maybe used as a para-aramid fiber. Conex (trademark ofTeijin Ltd.), Nomex (trademark of E.I. Du Pont de Nemours & Co.) or thelike may be used as a meta-aramid fiber.

As shown in FIG. 2, some of the short aramid fibers 8, 8, . . . embeddedin each of the ribs 7 are extruded from the side face 11 of the rib 7.Extruded sections 15, 15, . . . of the short aramid fibers 8, 8, . . .are bowed over the entire side face 11 of the rib 7 to increase theirexposure areas and thereby cover the major part of the side face 11.Further, the extruded sections 15, 15, . . . of the short aramid fibers8, 8, . . . are bowed not in a single direction but irregularly inmultiple different directions. Thus, since the plurality of extrudedfiber sections 15, 15, . . . are bowed in various direction todecentralized their orientation, the wearing property of the V-ribbedbelt 10 is enhanced uniformly in every direction. Accordingly, theV-ribbed belt 10 is independent of its running direction and can exhibituniform performance in either running direction.

Next, the shape of the extruded section 15 of each short aramid fiber 8will be described in detail with reference to FIG. 3. The root portion12 of the extruded section 15 of the short aramid fiber 8 is raised fromthe side face 11 of the rib 7. In other words, the root portion 12 ofthe extruded fiber section 15 is in substantially upright position withrespect to the side face 11 of the rib 7. The medial portion 13 of theextruded fiber section 15 is bowed from the end of the root portion 12.The tip portion 14 of the extruded fiber section 15 is bowed in adirection different from the bowing direction of the medial portion 13.For example, in the short aramid fiber 8 shown in FIG. 3, the tipportion 14 is bowed in a direction opposite to the bowing direction ofthe medial portion 13. Thus, the extruded short aramid fiber 8 is bowedin two steps. Specifically, the extruded section 15 of the short aramidfiber 8 is formed in such a curled shape as bowed first in a certaindirection and then opposite direction on its way from root to tip. As aresult, the extruded short aramid fiber 8 is kept elevated above theside face 11 of the rib 7. Accordingly, the short aramid fiber 8 canexert a restoring force like a leaf spring in association with itscurled shape. In addition, microscopic unevenness can be formed over theside face of the rib 7 so that the root portions 12 of short fibersconstitute microscopic convexities.

The length of the extruded section 15 of the short aramid fiber 8 ispreferably 50 μm or less. By friction with a grinding wheel during agrinding process described later, some of the extruded sections 15, 15,. . . of the short aramid fibers 8, 8, . . . are flattened and othersare cracked at the tips thereof as shown in FIG. 4.

Fabricating Method of V-ribbed Belt

A method for fabricating the V-ribbed belt 10 will be described next.

First, an unvulcanized rubber sheet for constituting the adhesion rubberlayer 4, a cord for constituting the tension member 2 and anotherunvulcanized rubber sheet into which short aramid fibers are mixed arestacked in this order, and these elements are hot cured therebyobtaining a molded form of belt in cylindrical shape.

Then, as shown in FIG. 5, the molded form of belt 19 is entrained aroundmain and tension rolls 22, 23 of a drive mechanism 20 and is run by thisdrive mechanism 20. In the figure, the reference numeral 24A denotes aguide roll. Next, the running molded form of belt 19 is pressed againsta grinding wheel 21 driven into rotation thereby grinding the moldedform of belt 19. In this case, the short aramid fibers 8 are hardly cutoff because of its large greige tensile module and some of them areextruded from the side faces 11 of the ribs 7. Specifically, when eachof the extruded short aramid fibers 8 is released from stress induced inits surface by interference with abrasives, it plastically deforms tobow its tip portion.

During this grinding process, the extruded section 15 of the shortaramid fiber 8 can be adjusted in its length, shape, degree of flatnessand cracked condition of the tip by controlling the type or pressingforce of the grinding wheel 21.

For the grinding wheel 21, use is preferably made of a construction inwhich diamond abrasives 24 are fixed on the periphery of a disk-likewheel 25 by electroplating, brazing, baking or the like. However,abrasives in the present invention is not limited to diamond abrasivesbut may be other super abrasives made of, for example, cubic boronnitride (CBN). FIG. 6(a) is a partly vertical projection of theperiphery of the wheel 25, and FIG. 6(b) is a cross-sectional view takenalong the line A—A of FIG. 6(a). As shown in these FIGS. 6(a) and 6(b),bond (such as metal bond or nickel bond) is spread and coated in a thinlayer on the periphery of the wheel 25 (see FIG. 5) to form a bondingpart 26.

The diamond abrasives 24 are distributed uniformly in and adhered to thebonding part 26. The grain size of the abrasive 24 is set preferably inthe range of #30 to #200, and at #140 in this embodiment. The height ofextrusion of each abrasive 24 is set preferably at 50 to 95% of itsentire height, and at 80% thereof in this embodiment. The density of theabrasives 24 (the rate at which the total surface area of the abrasivesoccupies with respect to the entire grinding surface area) is setpreferably in the range of 3.5 to 55%, and at 45% in this embodiment.

The rotation of the wheel 25 in the grinding process is made preferablyat a peripheral speed of between 500 and 2000 m/min, and at a peripheralspeed of 1000 m/min in this embodiment. The grinding speed ratio Vs/Vw,which is a ratio of the peripheral speed Vs of the grinding wheel 21 tothe peripheral speed Vw of the belt 19, is set preferably in the rangeof 0.002 to 0.04, and at 0.004 in this embodiment.

Effects of this Embodiment

As can be seen from the above, since the extruded sections 15 of theshort aramid fibers 8 in the V-ribbed belt 10 are plastically deformedinto bowed shape, the total surface area of the extruded short aramidfibers 8 is large with respect to the area of the side face 11 of therib 7. This enhances the wearing property of the V-ribbed belt 10.

Further, since some of the extruded short aramid fibers 8 are flattenedor cracked at their tips, they further increase their surface areas.This further enhances the wearing property of the V-ribbed belt 10. If ashort fiber is fibrillated at its end, its intrinsic strength maybeimpaired. The short fibers in this embodiment, however, are crackedwithout fibrillation. That is, the crack of the short aramid fiber 8 inthis inventive belt 10 is a line of the short fiber broken at a moremacroscopic level than fibrillated. Accordingly, the short aramid fibers8 are not impaired in their intrinsic strengths.

Since the short aramid fibers 8, 8, . . . are bowed in multipledirections, their performance can be exhibited independent of therunning direction of the belt 10. Therefore, when the belt 10 grips ormoves away from a pulley, stable frictional resistance can beestablished in friction surfaces of the belt 10 and the pulley. As aresult, variations in frictional resistance can be reduced therebystabilizing the running of the belt 10. Accordingly, the V-ribbed belt10 in this embodiment can exhibit bearing strength and wearing propertyuniformly in either running direction.

Since the medial and tip portions 13, 14 of the extruded section 15 ofthe short aramid fiber 8 are bowed in different directions, the extrudedsection 15 of the short aramid fiber 8 has a restoring force like a leafspring. As a result, the restoring forces of the short aramid fibers 8can absorb variations in pressure applied to the V-ribbed belt 10.Accordingly, the running of the belt 10 is further stabilized so thatthe belt 10 can transmit power with increased stability. In addition,the restoring forces can relax the stresses placed on the root portions12 of the extruded short aramid fibers 8. Accordingly, the short aramidfibers 8 can be prevented from dropping out thereby suppressingdeterioration of the V-ribbed belt 10.

Since the root portions 12 of the extruded short aramid fibers 8 areraised from the side face 11 of the rib 7, microscopic unevenness isformed over the side face 11 of the rib 7 so that the root portions 12constitute microscopic convexities. This enables to effectively preventthe occurrence of noise. According to the method for fabricating aV-ribbed belt in this embodiment, since grinding is made using superabrasives each extruded for 50 to 95% of their grain size from thebonding part 26, a contact between the boding part 26 and the rib 7 ishard to occur during grinding. Therefore, an amount of heat produced byfriction is small, which enables successful grinding. Further, sincediamond of relatively high heat conductivity is used as a material ofsuper abrasives, heat production can be effectively suppressed.

Since the density of super abrasives is relatively as low as 3.5 to 55%,clearances between the abrasives, i.e., chip pockets, are large in size.Therefore, clogging between the abrasives due to the chips is difficultto occur during grinding. Accordingly, heat production due to suchclogging hardly occur, which enables successful grinding.

Furthermore, since use is made of the wheel 25 with super abrasiveshaving a large height of extrusion and a small density, the short aramidfibers 8 can be easily extruded for relatively large lengths from theside face 11 of the rib 7. In addition, the extruded section 15 can beeasily formed in curled shape with its root portion 12 assuming anupright position.

Performance Comparison

Next, description will be made about a performance comparison test forcomparing performances of the V-ribbed belt 10 in this embodiment and aconventional V-ribbed belt. As the conventional V-ribbed belt, use wasmade of a V-ribbed belt in which extruded short aramid fibers extendlinearly. In this test, a weight weighing W was suspended from a loadcell 31 through a guide roller 33 by a sample belt 32 as shown in FIG.7, respective tensions T1 and T2 at tight and slack sides of the belt 32were measured by detecting a value of the load cell 31, and changes ofthe ratio (tension ratio) T1/T2 with time were determined. It is to benoted that the tension ratio T1/T2 provides an indication of thecoefficient of friction μ=(1/π)ln(T1/T2).

As shown in FIG. 8, the test results showed that the V-ribbed belt 10 inthis embodiment decreased variations of the tension ratio T1/T2 ascompared with conventional one. Further, a comparison of the tensionratios T1/T2 of both the belts having been continuously run for 24 hoursshowed that the V-ribbed belt 10 in this embodiment was smaller invariations of the tension ratio T1/T2 as compared with conventional one,as shown in FIG. 9. Accordingly, it can be understood that the V-ribbedbelt 10 in this embodiment is excellent not only in initial performancebut also in performance after its running as compared with theconventional V-ribbed belt.

The reason for this seems as follows. Since the conventional V-ribbedbelt has its extruded short aramid fibers oriented in a singledirection, its frictional resistance is stable with respect to a normaldirection but tends to increase with respect to a reverse direction.Therefore, if tension applied to the belt is changed from the normaldirection to the reverse direction, frictional resistance of the belt islargely changed even by a slight variation of tension, resulting ininducing a large variation of tension. On the other hand, since theV-ribbed belt 10 in this embodiment has its extruded short aramid fibers8, 8, . . . irregularly bowed in multiple directions, a change of itsfrictional resistance associated with a slight variation of tension issmall. Accordingly, the variation of tension is not increased and thetension ratio is stable.

Meanwhile, if a variation of frictional resistance of the belt is large,the belt is easy to cause chattering. Another performance comparisontest was conducted for belt chattering at the start of running with theuse of the V-ribbed belt in this embodiment and a conventional V-ribbedbelt in which extruded short aramid fibers were bent in a givendirection. Since a belt may be used under conditions where water or oilenters between its rib and a pulley depending upon use environments,measurements of chattering of both the V-ribbed belts were made not onlyin their initial conditions but also under water-inpouring conditions.As shown in FIG. 10, the test results showed that the V-ribbed belt 10in this embodiment caused very small chattering. The main reason forthis seems that the V-ribbed belt 10 in this embodiment has a smallamount of variation in tension ratio as described above.

The test results also showed that while the conventional belt increasedthe chattering level under water-inpouring conditions, the V-ribbed belt10 in this embodiment was low in chattering level even under the sameconditions. The reason for this seems as follows. Since the short aramidfibers 8 of the V-ribbed belt 10 in this embodiment have extrudedsections 15 formed in curled shape and upright root portions 12, waterpouring onto the side face 11 of the rib 7 readily passes throughclearances between the root portions 12 of the short aramid fibers 8.Accordingly, water is hardly retained on the side face 11 of the rib 7and readily smoothly discharged therefrom. For this reason, it seemsthat the occurrence of chattering in the V-ribbed belt 10 of thisembodiment is suppressed also under water-inpouring conditions incontrast to the conventional belt.

Embodiment 2

FIG. 11 shows a cross section of a power transmission belt 10 accordingto Embodiment 2 of the present invention.

In this embodiment, a plurality of short aramid fibers 8, 8, . . . and aplurality of non-aramid synthetic fibers 38, 38, . . . are mixed intoeach of ribs 7 while maintaining their orientation to a given direction.Particularly in this embodiment, short aramid fibers 8 and non-aramidsynthetic fibers 38 are embedded into the ribs 7 while maintaining theirorientation to a belt widthwise direction (lateral direction in FIG.11).

Like Embodiment 1, the short aramid fiber 8 may be made of a para-aramidor meta-aramid fiber. For the synthetic fiber 38, suitable use can bemade of nylon, vinylon, polyester or the like with a filament diameterof 20 μm or more.

As shown in. FIGS. 12 and 13, microscopic unevenness (for example, witha level difference of 0.5 to 10 μm) is formed in the surface 11 of therib 7. In this embodiment, the surface unevenness of the rib is formedin such a configuration that a plurality of waves are traveled in asingle direction by a wind, i.e., in wavy shape. However, it goeswithout saying that the surface unevenness of the rib in the presentinvention is not limited to such wavy shape but maybe an unevenconfiguration 46 in which peaks and valleys are alternately disposed asshown in FIG. 14 or other uneven configurations.

As shown in FIGS. 12 and 13, some of the crowd of short aramid fibers 8,8, . . . embedded in each of the ribs 7 are extruded from the surface 11of the rib 7. An extruded section 15 of each short aramid fiber 8 isbowed to increase its apparent surface area per unit extruded height.Further, the extruded sections 15, 15, . . . of the short aramid fibers8, 8, . . . are bowed not in the same direction but randomly in multipledirections. Since the extruded fiber sections 15, 15, . . . are thusbowed in various directions to decentralized their orientation, thebearing strength and wearing property of the V-ribbed belt 10 areenhanced uniformly in every direction like Embodiment 1. Accordingly,the V-ribbed belt 10 is independent of its running direction and canexhibit uniform performance in either running direction.

As shown in FIG. 13, the extruded section 15 of each aramid fiber 8 inthis embodiment has the same configuration as that in Embodiment 1.Furthermore, in this embodiment, some of the crowd of synthetic fibers38, 38, . . . embedded in each of the ribs 7 are also extruded from theside face 11 of the rib 7. However, extruded sections 40, 40, . . . ofthe synthetic fibers 38, 38, . . . are inclined in a given directionunlike the extruded sections 15, 15, . . . of the short aramid fibers 8,8, . . . Specifically, each of the extruded sections 40 is inclined in adirection opposed to wave fronts 45 in the wavy-shaped side face 11 ofeach rib 7. And, the extruded section 40 of the synthetic fiber 38 isformed in a sector gradually flattened and broadened toward its end. Thecorners of the sector are rounded to present gently curved surfaces.Also, the extruded section 40 of the synthetic fiber 38 is kept innon-melting condition and formed at its end in the shape of waves.

As shown in FIG. 13, the root portion of the extruded section 40 of thesynthetic fiber 38 is likewise raised from the side face 11 of the rib7. As a result, microscopic unevenness can be also formed over thesurface of the rib 7 so that the extruded sections 15, 40 of shortaramid fibers 8 and synthetic fibers 38 constitute microscopicconvexities and surface regions adjoining places where the short fibers8, 38 are implanted constitute microscopic concavities, separately fromthe microscopic unevenness formed in the side face 11 of the rib 7.

Fabricating Method of V-ribbed Belt

The V-ribbed belt 10 in this embodiment is fabricated in the followingmanner.

First, an unvulcanized rubber sheet for constituting a adhesion rubberlayer 4, a cord for constituting a tension member 2 and anotherunvulcanized rubber sheet into which short aramid fibers and syntheticfibers are mixed are stacked in this order, and these elements are hotcured thereby obtaining a molded form of belt in cylindrical shape.

Then, in the same manner as in Embodiment 1 (see FIG. 5), the moldedform of belt 19 is entrained around main and tension rolls 22, 23 of adrive mechanism 20 and is run by this drive mechanism 20. Next, therunning molded form of belt 19 is pressed against a grinding wheel 21driven into rotation thereby grinding the molded form of belt 19. Inthis case, the short aramid fibers 8 are hardly cut off because of itslarge greige tensile module and some of them are extruded for relativelylarge lengths from the side faces 11 of the ribs 7. Further, some of thesynthetic fibers 38 are extruded in positions inclined reversely to thebelt running direction. Specifically, each of the extruded short aramidfibers 8 and synthetic fibers 38 is released from stress induced in itssurface by interference with abrasives thereby plastically deforming.Then, the surface of each rib 7 is formed in the shape of waves suchthat their wave fronts 45 are directed to the direction of rotation ofthe grinding wheel 21.

During this grinding process, the extruded configurations of the shortaramid fiber 8 and synthetic fiber 38 and the uneven surfaceconfiguration of the rib 7 can be adjusted by controlling the type orpressing force of the grinding wheel 21. In this embodiment, grinding ismade under the same conditions and with the same grinding wheel 21 asused in Embodiment 1.

Effects of this Embodiment

According to the V-ribbed belt 10 in this embodiment as described above,since microscopic unevenness is formed in the side face 11 of each rib7, the surface area of the rubber portion of the rib 7 is large. Thisenables to reduce bearing stress on the surface of the rubber portion.Accordingly, wear of the rubber portion can be suppressed, resulting inimproved friction property and elongated life time of the belt.

If water or oil enters between a pulley and a belt, frictionalresistance of the belt generally becomes unstable. In the V-ribbed belt10 of this embodiment, however, microscopic unevenness is formed overthe side face 11 of each rib 7. Accordingly, microscopic clearances areformed between the belt and a pulley. Therefore, water or the like isdistributed among the clearances and then readily discharged through theclearances, which stabilizes frictional resistance of the belt.

Since the short aramid fibers 8 and synthetic fibers 38 are extrudedfrom the side face 11 of each rib 7, the rib 7 itself is hardly worn andits surface is hardly flattened. Accordingly, the belt can exhibit for along time the above effects obtained by forming the rib surface intouneven configuration.

Further, each rib 7 has unevenness in the side face 11 itself.Therefore, even if the rib 7 itself is worn due to extended periods ofuse, the belt can be expected to continue to exhibit the above effectsunless the uneven surface has been worn out into flatness. Accordingly,the V-ribbed belt 10 in this embodiment can retain its high performancefor a long time.

Performance Comparison

Next, description will be made about a performance comparison test forcomparing performances of the V-ribbed belt 10 in this embodiment and aV-ribbed belt (comparative example) in which the side face 11 of eachrib 7 is formed with no unevenness. In this test, a weight weighing Wwas suspended from a load cell 31 through a guide roller 33 by a samplebelt 32 as shown in FIG. 15, respective tensions T1 and T2 at tight andslack sides of the belt 32 were measured by detecting a value of theload cell 31, and a frictional force of the belt 32 was determined fromthe ratio (tension ratio) T1/T2.

As shown in FIG. 16, the test results showed that the V-ribbed belt 10in this embodiment was about 25% smaller in frictional force than thecomparative example. Further, the same test was conducted under theconditions where water was inpoured between the guide roller 33 and thesample belt 32. The test result showed that, as shown in FIG. 17, theV-ribbed belt 10 in this embodiment was about 30% smaller in frictionalforce than the comparative example.

Modifications

The present invention is not limited to the V-ribbed belts 10 asdescribed in the above embodiments but may be V-ribbed belts of othertypes. For example, a joined V-ribbed belt 10A as shown in FIG. 18 isalso applicable. Further, power transmission belts of other types suchas V-belts are also applicable.

What is claimed is:
 1. A power transmission belt in which a plurality ofshort fibers are mixed into a compression rubber thereof so as to beoriented in a given direction, some of the short fibers each having aprotruded section extending from a surface of the compression rubber,wherein root portions of at least most of the short fibers are kept offof the surface of the compression rubber, and protruded sections of atleast most of the short fibers are raised from the surface of thecompression rubber and then bowed.
 2. The power transmission belt ofclaim 1, wherein the protruded sections of the short fibers are bowedfirst in one direction and then another direction on the way from a rootto a tip thereof.
 3. The power transmission belt of claims 1 or 2,wherein at least the tip of the protruded sections of the short fibersare flattened.
 4. The power transmission belt of claims 1 or 2, whereinthe tip of the protruded sections of the short fibers are cracked byplastic deformation.
 5. The power transmission belt of claims 1 or 2,wherein the protruded sections of the short fibers are different inbowing direction from one another to decentralize the orientationthereof.
 6. The power transmission belt of claim 1 or 2, wherein theshort fibers are made of para-aramid fibers or meta-aramid fibers.